Chen confessed getting a surgery that not even the members knew he'd gotten.

On the December 7th episode of 'Knowing Brothers', Chen confessed that he had gotten his lingual frenulum cut when he was in high school. He said, "I wanted to sing really well in high school. Just like getting a teeth laminate, it's irreversible."

He then said, "I regretted it a lot. I felt like my pronunciation was getting rigid. I heard that it was a light surgery, but it hurt a lot. I couldn't even swallow. And I learned it doesn't even have anything to do with your singing ability."